Navigator
object
Support in all current engines.
Support in all current engines.
The
navigator
attribute
of
the
Window
interface
must
return
an
instance
of
the
Navigator
interface,
which
represents
the
identity
and
state
of
the
user
agent
(the
client),
and
allows
web
pages
to
register
themselves
as
potential
protocol
handlers:
[Exposed=Window]
interface Navigator {
// objects implementing this interface also implement the interfaces given below
};
Navigator includes NavigatorID;
Navigator includes NavigatorLanguage;
;
Navigator includes NavigatorOnLine;
Navigator includes NavigatorContentUtils;
Navigator includes NavigatorCookies;
Navigator includes NavigatorPlugins;
Navigator
includes
NavigatorConcurrentHardware
;
These
interface
mixins
are
defined
separately
so
that
WorkerNavigator
can
re-use
parts
of
the
Navigator
interface.
Support in all current engines.
interface mixin NavigatorID {
readonly attribute DOMString appCodeName; // constant "Mozilla"
readonly attribute DOMString appName; // constant "Netscape"
readonly attribute DOMString appVersion;
readonly attribute DOMString platform;
readonly attribute DOMString product; // constant "Gecko"
[Exposed=Window] readonly attribute DOMString productSub;
readonly attribute DOMString userAgent;
[Exposed=Window] readonly attribute DOMString vendor;
[Exposed=Window] readonly attribute DOMString vendorSub; // constant ""
};
In certain cases, despite the best efforts of the entire industry, web browsers have bugs and limitations that web authors are forced to work around.
This section defines a collection of attributes that can be used to determine, from script, the kind of user agent in use, in order to work around these issues.
The user agent has a navigator compatibility mode , which is either Chrome , Gecko , or WebKit .
The
navigator
compatibility
mode
constrains
the
NavigatorID
interface
to
the
combinations
of
attribute
values
and
presence
of
taintEnabled()
and
oscpu
that
are
known
to
be
compatible
with
existing
web
content.
Client detection should always be limited to detecting known current versions; future versions and unknown versions should always be assumed to be fully compliant.
navigator
.
appCodeName
Returns
the
string
"
Mozilla
".
navigator
.
appName
Returns
the
string
"
Netscape
".
navigator
.
appVersion
Returns the version of the browser.
navigator
.
platform
Returns the name of the platform.
navigator
.
product
Returns
the
string
"
Gecko
".
navigator
.
productSub
Returns
either
the
string
"
20030107
",
or
the
string
"
20100101
".
navigator
.
userAgent
Returns
the
complete
`
User-Agent
`
header.
navigator
.
vendor
Returns
either
the
empty
string,
the
string
"
Apple
Computer,
Inc.
",
or
the
string
"
Google
Inc.
".
navigator
.
vendorSub
Returns the empty string.
appCodeName
Must
return
the
string
"
Mozilla
".
appName
Must
return
the
string
"
Netscape
".
appVersion
Must
return
either
the
string
"
4.0
"
or
a
string
representing
the
version
of
the
browser
in
detail,
e.g.
"
1.0
(VMS;
en-US)
Mellblomenator/9000
".
platform
Must
return
either
the
empty
string
or
a
string
representing
the
platform
on
which
the
browser
is
executing,
e.g.
"
MacIntel
",
"
Win32
",
"
FreeBSD
i386
",
"
WebTV
OS
".
product
Must
return
the
string
"
Gecko
".
productSub
Must return the appropriate string from the following list:
The
string
"
20030107
".
The
string
"
20100101
".
userAgent
Support in all current engines.
Must
return
the
default
`
User-Agent
`
value
.
vendor
Support in all current engines.
Must return the appropriate string from the following list:
The
string
"
Google
Inc.
".
The empty string.
The
string
"
Apple
Computer,
Inc.
".
vendorSub
Must return the empty string.
If the navigator compatibility mode is Gecko , then the user agent must also support the following partial interface:
partial interface mixin NavigatorID {
[Exposed=Window] boolean taintEnabled(); // constant false
[Exposed=Window] readonly attribute DOMString oscpu;
};
The
taintEnabled()
method
must
return
false.
The
oscpu
attribute's
getter
must
return
either
the
empty
string
or
a
string
representing
the
platform
on
which
the
browser
is
executing,
e.g.
"
Windows
NT
10.0;
Win64;
x64
",
"
Linux
x86_64
".
Any information in this API that varies from user to user can be used to profile the user. In fact, if enough such information is available, a user can actually be uniquely identified. For this reason, user agent implementers are strongly urged to include as little information in this API as possible.
Support in all current engines.
interface mixin NavigatorLanguage {
readonly attribute DOMString language;
readonly attribute FrozenArray<DOMString> languages;
};
navigator
.
language
Returns a language tag representing the user's preferred language.
navigator
.
languages
Returns an array of language tags representing the user's preferred languages, with the most preferred language first.
The
most
preferred
language
is
the
one
returned
by
navigator.language
.
A
languagechange
event
is
fired
at
the
Window
or
WorkerGlobalScope
object
when
the
user
agent's
understanding
of
what
the
user's
preferred
languages
are
changes.
language
Support in all current engines.
Must return a valid BCP 47 language tag representing either a plausible language or the user's most preferred language. [BCP47]
languages
Support in all current engines.
Must return a frozen array of valid BCP 47 language tags representing either one or more plausible languages , or the user's preferred languages, ordered by preference with the most preferred language first. The same object must be returned until the user agent needs to return different values, or values in a different order. [BCP47]
Whenever
the
user
agent
needs
to
make
the
navigator.languages
attribute
of
a
Window
or
WorkerGlobalScope
object
global
return
a
new
set
of
language
tags,
the
user
agent
must
queue
a
global
task
on
the
DOM
manipulation
task
source
given
global
to
fire
an
event
named
languagechange
at
global
,
and
wait
until
that
task
begins
to
be
executed
before
actually
returning
a
new
value.
To determine a plausible language , the user agent should bear in mind the following:
en-US
"
is
suggested;
if
all
users
of
the
service
use
that
same
value,
that
reduces
the
possibility
of
distinguishing
the
users
from
each
other.
To
avoid
introducing
any
more
fingerprinting
vectors,
user
agents
should
use
the
same
list
for
the
APIs
defined
in
this
function
as
for
the
HTTP
`
Accept-Language
`
header.
Support in all current engines.
interface mixin NavigatorOnLine {
readonly attribute boolean onLine;
};
navigator
.
onLine
Returns false if the user agent is definitely offline (disconnected from the network). Returns true if the user agent might be online.
The
events
online
and
offline
are
fired
when
the
value
of
this
attribute
changes.
Support in all current engines.
The
navigator.onLine
attribute
must
return
false
if
the
user
agent
will
not
contact
the
network
when
the
user
follows
links
or
when
a
script
requests
a
remote
page
(or
knows
that
such
an
attempt
would
fail),
and
must
return
true
otherwise.
When
the
value
that
would
be
returned
by
the
navigator.onLine
attribute
of
a
Window
or
WorkerGlobalScope
global
changes
from
true
to
false,
the
user
agent
must
queue
a
global
task
on
the
networking
task
source
given
global
to
fire
an
event
named
offline
at
global
.
On
the
other
hand,
when
the
value
that
would
be
returned
by
the
navigator.onLine
attribute
of
a
Window
or
WorkerGlobalScope
global
changes
from
false
to
true,
the
user
agent
must
queue
a
global
task
on
the
networking
task
source
given
global
to
fire
an
event
named
online
at
the
Window
or
WorkerGlobalScope
object.
This attribute is inherently unreliable. A computer can be connected to a network without having Internet access.
In this example, an indicator is updated as the browser goes online and offline.
<!DOCTYPE HTML>
<html lang="en">
<head>
<title>Online status</title>
<script>
function updateIndicator() {
document.getElementById('indicator').textContent = navigator.onLine ? 'online' : 'offline';
}
</script>
</head>
<body onload="updateIndicator()" ononline="updateIndicator()" onoffline="updateIndicator()">
<p>The network is: <span id="indicator">(state unknown)</span>
</body>
</html>
registerProtocolHandler()
method
Navigator/registerProtocolHandler
interface mixin NavigatorContentUtils {
[SecureContext] undefined registerProtocolHandler(DOMString scheme, USVString url);
[SecureContext] undefined unregisterProtocolHandler(DOMString scheme, USVString url);
};
navigator
.
registerProtocolHandler
(
scheme
,
url
)
Registers
a
handler
for
scheme
at
url
.
For
example,
an
online
telephone
messaging
service
could
register
itself
as
a
handler
of
the
sms:
scheme,
so
that
if
the
user
clicks
on
such
a
link,
they
are
given
the
opportunity
to
use
that
web
site.
[SMS]
The
string
"
%s
"
in
url
is
used
as
a
placeholder
for
where
to
put
the
URL
of
the
content
to
be
handled.
Throws
a
"
SecurityError
"
DOMException
if
the
user
agent
blocks
the
registration
(this
might
happen
if
trying
to
register
as
a
handler
for
"
http
",
for
instance).
Throws
a
"
SyntaxError
"
DOMException
if
the
"
%s
"
string
is
missing
in
url
.
navigator
.
unregisterProtocolHandler
(
scheme
,
url
)
Unregisters the handler given by the arguments.
Throws
a
"
SecurityError
"
DOMException
if
the
user
agent
blocks
the
deregistration
(this
might
happen
if
with
invalid
schemes,
for
instance).
Throws
a
"
SyntaxError
"
DOMException
if
the
"
%s
"
string
is
missing
in
url
.
The
registerProtocolHandler(
scheme
,
url
)
method
steps
are:
Let ( normalizedScheme , normalizedURLString ) be the result of running normalize protocol handler parameters with scheme , url , and this 's relevant settings object .
In parallel : register a handler for normalizedScheme and normalizedURLString . User agents may, within the constraints described, do whatever they like. A user agent could, for instance, prompt the user and offer the user the opportunity to add the site to a shortlist of handlers, or make the handlers their default, or cancel the request. User agents could also silently collect the information, providing it only when relevant to the user.
User agents should keep track of which sites have registered handlers (even if the user has declined such registrations) so that the user is not repeatedly prompted with the same request.
When the user agent uses this handler for a URL inputURL :
Assert: inputURL 's scheme is normalizedScheme .
Let inputURLString be the serialization of inputURL .
Let encodedURL be the result of running UTF-8 percent-encode on inputURLString using the component percent-encode set .
Let handlerURLString be normalizedURLString .
Replace
the
first
instance
of
"
%s
"
in
handlerURLString
with
encodedURL
.
Let resultURL be the result of parsing handlerURLString .
Navigate an appropriate browsing context to resultURL .
If
the
user
had
visited
a
site
at
https://example.com/
that
made
the
following
call:
navigator.registerProtocolHandler('web+soup',
'soup?url=%s')
...and
then,
much
later,
while
visiting
https://www.example.net/
,
clicked
on
a
link
such
as:
<a
href="web+soup:chicken-kïwi">Download
our
Chicken
Kïwi
soup!</a>
...then the UA might navigate to the following URL:
https://example.com/soup?url=web+soup:chicken-k%C3%AFwi
This site could then do whatever it is that it does with soup (synthesize it and ship it to the user, or whatever).
This does not define when the handler is used. To some extent, the processing model for navigating across documents defines some cases where it is relevant, but in general user agents may use this information wherever they would otherwise consider handing schemes to native plugins or helper applications.
The
unregisterProtocolHandler(
scheme
,
url
)
method
steps
are:
Let ( normalizedScheme , normalizedURLString ) be the result of running normalize protocol handler parameters with scheme , url , and this 's relevant settings object .
In parallel : unregister the handler described by normalizedScheme and normalizedURLString .
To normalize protocol handler parameters , given a string scheme , a string url , and an environment settings object environment , run these steps:
Set scheme to scheme , converted to ASCII lowercase .
If
scheme
is
neither
a
safelisted
scheme
nor
a
string
starting
with
"
web+
"
followed
by
one
or
more
ASCII
lower
alphas
,
then
throw
a
"
SecurityError
"
DOMException
.
This
means
that
including
a
colon
in
scheme
(as
in
"
mailto:
")
will
throw.
The following schemes are the safelisted schemes :
bitcoin
geo
im
irc
ircs
magnet
mailto
mms
news
nntp
openpgp4fpr
sip
sms
smsto
ssh
tel
urn
webcal
wtai
xmpp
This list can be changed. If there are schemes that ought to be added, please send feedback.
If
url
does
not
contain
"
%s
",
then
throw
a
"
SyntaxError
"
DOMException
.
Parse url relative to environment .
If
that
fails,
then
throw
a
"
SyntaxError
"
DOMException
.
This
is
forcibly
the
case
if
the
%s
placeholder
is
in
the
host
or
port
of
the
URL.
If
the
resulting
URL
record
's
scheme
is
not
"
https
"
or
the
resulting
URL
record
's
origin
is
not
same
origin
with
environment
's
origin
,
then
throw
a
"
SecurityError
"
DOMException
.
Return ( scheme , resulting URL string ).
The
resulting
URL
string
will
by
definition
not
be
a
valid
URL
string
as
it
includes
the
string
"
%s
"
which
is
not
a
valid
component
in
a
URL.
Custom scheme handlers can introduce a number of concerns, in particular privacy concerns.
Hijacking all web usage. User agents should not allow schemes that are key to its normal operation, such as an HTTP(S) scheme , to be rerouted through third-party sites. This would allow a user's activities to be trivially tracked, and would allow user information, even in secure connections, to be collected.
Hijacking defaults. User agents are strongly urged to not automatically change any defaults, as this could lead the user to send data to remote hosts that the user is not expecting. New handlers registering themselves should never automatically cause those sites to be used.
Registration
spamming.
User
agents
should
consider
the
possibility
that
a
site
will
attempt
to
register
a
large
number
of
handlers,
possibly
from
multiple
domains
(e.g.,
by
redirecting
through
a
series
of
pages
each
on
a
different
domain,
and
each
registering
a
handler
for
web+spam:
—
analogous
practices
abusing
other
web
browser
features
have
been
used
by
pornography
web
sites
for
many
years).
User
agents
should
gracefully
handle
such
hostile
attempts,
protecting
the
user.
Hostile handler metadata. User agents should protect against typical attacks against strings embedded in their interface, for example ensuring that markup or escape characters in such strings are not executed, that null bytes are properly handled, that over-long strings do not cause crashes or buffer overruns, and so forth.
Leaking private data. Web page authors may reference a custom scheme handler using URL data considered private. They might do so with the expectation that the user's choice of handler points to a page inside the organization, ensuring that sensitive data will not be exposed to third parties. However, a user may have registered a handler pointing to an external site, resulting in a data leak to that third party. Implementors might wish to consider allowing administrators to disable custom handlers on certain subdomains, content types, or schemes.
Leaking credentials. User agents must never send username or password information in the URLs that are escaped and included sent to the handler sites. User agents may even avoid attempting to pass to web-based handlers the URLs of resources that are known to require authentication to access, as such sites would be unable to access the resources in question without prompting the user for credentials themselves (a practice that would require the user to know whether to trust the third-party handler, a decision many users are unable to make or even understand).
Interface interference. User agents should be prepared to handle intentionally long arguments to the methods. For example, if the user interface exposed consists of an "accept" button and a "deny" button, with the "accept" binding containing the name of the handler, it's important that a long name not cause the "deny" button to be pushed off the screen.
interface mixin NavigatorCookies {
readonly attribute boolean cookieEnabled;
};
navigator
.
cookieEnabled
Returns false if setting a cookie will be ignored, and true otherwise.
Support in all current engines.
The
cookieEnabled
attribute
must
return
true
if
the
user
agent
attempts
to
handle
cookies
according
to
HTTP
State
Management
Mechanism
,
and
false
if
it
ignores
cookie
change
requests.
[COOKIES]
Support in all current engines.
Support in all current engines.
Support in all current engines.
Support in all current engines.
Support in all current engines.
interface mixin NavigatorPlugins {
[SameObject] readonly attribute PluginArray plugins;
[SameObject] readonly attribute MimeTypeArray mimeTypes;
boolean javaEnabled();
};
[Exposed=Window,
LegacyUnenumerableNamedProperties]
interface PluginArray {
undefined refresh(optional boolean reload = false);
readonly attribute unsigned long length;
getter Plugin? item(unsigned long index);
getter Plugin? namedItem(DOMString name);
};
[Exposed=Window,
LegacyUnenumerableNamedProperties]
interface MimeTypeArray {
readonly attribute unsigned long length;
getter MimeType? item(unsigned long index);
getter MimeType? namedItem(DOMString name);
};
[Exposed=Window,
LegacyUnenumerableNamedProperties]
interface Plugin {
readonly attribute DOMString name;
readonly attribute DOMString description;
readonly attribute DOMString filename;
readonly attribute unsigned long length;
getter MimeType? item(unsigned long index);
getter MimeType? namedItem(DOMString name);
};
[Exposed=Window]
interface MimeType {
readonly attribute DOMString type;
readonly attribute DOMString description;
readonly attribute DOMString suffixes; // comma-separated
readonly attribute Plugin enabledPlugin;
};
navigator
.
plugins
.
refresh
(
[
refresh
]
)
Updates the lists of supported plugins and MIME types for this page, and reloads the page if the lists have changed.
navigator
.
plugins
.
length
Returns
the
number
of
plugins,
represented
by
Plugin
objects,
that
the
user
agent
reports.
navigator
.
plugins
.
item
(
index
)
navigator
.
plugins
[
index
]
Returns
the
specified
Plugin
object.
navigator
.
plugins
.
item
(
name
)
navigator
.
plugins
[
name
]
Returns
the
Plugin
object
for
the
plugin
with
the
given
name.
navigator
.
mimeTypes
.
length
Returns
the
number
of
MIME
types,
represented
by
MimeType
objects,
supported
by
the
plugins
that
the
user
agent
reports.
navigator
.
mimeTypes
.
item
(
index
)
navigator
.
mimeTypes
[
index
]
Returns
the
specified
MimeType
object.
navigator
.
mimeTypes
.
item
(
name
)
navigator
.
mimeTypes
[
name
]
Returns
the
MimeType
object
for
the
given
MIME
type.
name
Returns the plugin's name.
description
Returns the plugin's description.
filename
Returns the plugin library's filename, if applicable on the current platform.
length
Returns
the
number
of
MIME
types,
represented
by
MimeType
objects,
supported
by
the
plugin.
item
(
index
)
Returns
the
specified
MimeType
object.
item
(
name
)
Returns
the
MimeType
object
for
the
given
MIME
type.
type
Returns the MIME type.
description
Returns the MIME type's description.
suffixes
Returns the MIME type's typical file extensions, in a comma-separated list.
enabledPlugin
Returns
the
Plugin
object
that
implements
this
MIME
type.
navigator
.
javaEnabled()
Returns
true
if
there's
a
plugin
that
supports
the
MIME
type
"
application/x-java-vm
".
Support in one engine only.
The
navigator.plugins
attribute
must
return
a
PluginArray
object.
Support in one engine only.
The
navigator.mimeTypes
attribute
must
return
a
MimeTypeArray
object.
A
PluginArray
object
represents
none,
some,
or
all
of
the
plugins
supported
by
the
user
agent,
each
of
which
is
represented
by
a
Plugin
object.
Each
of
these
Plugin
objects
may
be
hidden
plugins
.
A
can't
be
enumerated,
but
can
still
be
inspected
by
using
its
name.
The
fewer
plugins
are
represented
by
the
PluginArray
object,
and
of
those,
the
more
that
are
,
the
more
the
user's
privacy
will
be
protected.
Each
exposed
plugin
increases
the
number
of
bits
that
can
be
derived
for
fingerprinting.
Hiding
a
plugin
helps,
but
unless
it
is
an
extremely
rare
plugin,
it
is
likely
that
a
site
attempting
to
derive
the
list
of
plugins
can
still
determine
whether
the
plugin
is
supported
or
not
by
probing
for
it
by
name
(the
names
of
popular
plugins
are
widely
known).
Therefore
not
exposing
a
plugin
at
all
is
preferred.
Unfortunately,
many
legacy
sites
use
this
feature
to
determine,
for
example,
which
plugin
to
use
to
play
video.
Not
exposing
any
plugins
at
all
might
therefore
not
be
entirely
plausible.
The
PluginArray
objects
created
by
a
user
agent
must
not
be
live
.
The
set
of
plugins
represented
by
the
objects
must
not
change
once
an
object
is
created,
except
when
it
is
updated
by
the
refresh()
method.
Each
plugin
represented
by
a
PluginArray
can
support
a
number
of
MIME
types
.
For
each
such
plugin
,
the
user
agent
must
pick
one
or
more
of
these
MIME
types
to
be
those
that
are
explicitly
supported
.
The
explicitly
supported
MIME
types
of
a
plugin
are
those
that
are
exposed
through
the
Plugin
and
MimeTypeArray
interfaces.
As
with
plugins
themselves,
any
variation
between
users
regarding
what
is
exposed
allows
sites
to
fingerprint
users.
User
agents
are
therefore
encouraged
to
expose
the
same
MIME
types
for
all
users
of
a
plugin
,
regardless
of
the
actual
types
supported...
at
least,
within
the
constraints
imposed
by
compatibility
with
legacy
content.
The
supported
property
indices
of
a
PluginArray
object
are
the
numbers
from
zero
to
the
number
of
non-
plugins
represented
by
the
object,
if
any.
The
length
attribute
must
return
the
number
of
non-
plugins
represented
by
the
object.
The
item()
method
of
a
PluginArray
object
must
return
null
if
the
argument
is
not
one
of
the
object's
supported
property
indices
,
and
otherwise
must
return
the
result
of
running
the
following
steps,
using
the
method's
argument
as
index
:
Let
list
be
the
Plugin
objects
representing
the
non-
plugins
represented
by
the
PluginArray
object.
Return the index th entry in list .
It is important for privacy that the order of plugins not leak additional information, e.g., the order in which plugins were installed.
The
supported
property
names
of
a
PluginArray
object
are
the
values
of
the
name
attributes
of
all
the
Plugin
objects
represented
by
the
PluginArray
object.
The
namedItem()
method
of
a
PluginArray
object
must
return
null
if
the
argument
is
not
one
of
the
object's
supported
property
names
,
and
otherwise
must
return
the
Plugin
object,
of
those
represented
by
the
PluginArray
object,
that
has
a
name
equal
to
the
method's
argument.
The
refresh()
method
of
the
PluginArray
object
of
a
Navigator
object,
when
invoked,
must
check
to
see
if
any
plugins
have
been
installed
or
reconfigured
since
the
user
agent
created
the
PluginArray
object.
If
so,
and
the
method's
argument
is
true,
then
the
user
agent
must
act
as
if
the
location.reload()
method
was
called
instead.
Otherwise,
the
user
agent
must
update
the
PluginArray
object
and
MimeTypeArray
object
created
for
attributes
of
that
Navigator
object,
and
the
Plugin
and
MimeType
objects
created
for
those
PluginArray
and
MimeTypeArray
objects,
using
the
same
Plugin
objects
for
cases
where
the
name
is
the
same,
and
the
same
MimeType
objects
for
cases
where
the
type
is
the
same,
and
creating
new
objects
for
cases
where
there
were
no
matching
objects
immediately
prior
to
the
refresh()
call.
Old
Plugin
and
MimeType
objects
must
continue
to
return
the
same
values
that
they
had
prior
to
the
update,
though
naturally
now
the
data
is
stale
and
may
appear
inconsistent
(for
example,
an
old
MimeType
entry
might
list
as
its
enabledPlugin
a
Plugin
object
that
no
longer
lists
that
MimeType
as
a
supported
MimeType
).
A
MimeTypeArray
object
represents
the
MIME
types
explicitly
supported
by
plugins
supported
by
the
user
agent,
each
of
which
is
represented
by
a
MimeType
object.
The
MimeTypeArray
objects
created
by
a
user
agent
must
not
be
live
.
The
set
of
MIME
types
represented
by
the
objects
must
not
change
once
an
object
is
created,
except
when
it
is
updated
by
the
PluginArray
object's
refresh()
method.
The
supported
property
indices
of
a
MimeTypeArray
object
are
the
numbers
from
zero
to
the
number
of
MIME
types
explicitly
supported
by
non-
plugins
represented
by
the
corresponding
PluginArray
object,
if
any.
The
length
attribute
must
return
the
number
of
MIME
types
explicitly
supported
by
non-
plugins
represented
by
the
corresponding
PluginArray
object,
if
any.
The
item()
method
of
a
MimeTypeArray
object
must
return
null
if
the
argument
is
not
one
of
the
object's
supported
property
indices
,
and
otherwise
must
return
the
result
of
running
the
following
steps,
using
the
method's
argument
as
index
:
Let
list
be
the
MimeType
objects
representing
the
MIME
types
explicitly
supported
by
non-
plugins
represented
by
the
corresponding
PluginArray
object,
if
any.
Return the index th entry in list .
It is important for privacy that the order of MIME types not leak additional information, e.g., the order in which plugins were installed.
The
supported
property
names
of
a
MimeTypeArray
object
are
the
values
of
the
type
attributes
of
all
the
MimeType
objects
represented
by
the
MimeTypeArray
object.
The
namedItem()
method
of
a
MimeTypeArray
object
must
return
null
if
the
argument
is
not
one
of
the
object's
supported
property
names
,
and
otherwise
must
return
the
MimeType
object
that
has
a
type
equal
to
the
method's
argument.
A
Plugin
object
represents
a
plugin
.
It
has
several
attributes
to
provide
details
about
the
plugin,
and
can
be
enumerated
to
obtain
the
list
of
MIME
types
that
it
explicitly
supports
.
The
Plugin
objects
created
by
a
user
agent
must
not
be
live
.
The
set
of
MIME
types
represented
by
the
objects,
and
the
values
of
the
objects'
attributes,
must
not
change
once
an
object
is
created,
except
when
updated
by
the
PluginArray
object's
refresh()
method.
The
reported
MIME
types
for
a
Plugin
object
are
the
MIME
types
explicitly
supported
by
the
corresponding
plugin
when
this
object
was
last
created
or
updated
by
refresh()
,
whichever
happened
most
recently.
The
supported
property
indices
of
a
Plugin
object
are
the
numbers
from
zero
to
the
number
of
reported
MIME
types
.
The
length
attribute
must
return
the
number
of
reported
MIME
types
.
The
item()
method
of
a
Plugin
object
must
return
null
if
the
argument
is
not
one
of
the
object's
supported
property
indices
,
and
otherwise
must
return
the
result
of
running
the
following
steps,
using
the
method's
argument
as
index
:
Let
list
be
the
MimeType
objects
representing
the
reported
MIME
types
.
Return the index th entry in list .
It is important for privacy that the order of MIME types not leak additional information, e.g., the order in which plugins were installed.
The
supported
property
names
of
a
Plugin
object
are
the
values
of
the
type
attributes
of
the
MimeType
objects
representing
the
reported
MIME
types
.
The
namedItem()
method
of
a
Plugin
object
must
return
null
if
the
argument
is
not
one
of
the
object's
supported
property
names
,
and
otherwise
must
return
the
MimeType
object
that
has
a
type
equal
to
the
method's
argument.
The
name
attribute
must
return
the
plugin
's
name.
The
description
and
filename
attributes
must
return
implementation-defined
(in
all
likelihood,
plugin
-defined)
strings.
In
each
case,
the
same
string
must
be
returned
each
time,
except
that
the
strings
returned
may
change
when
the
refresh()
method
updates
the
object.
If
the
values
returned
by
the
description
or
filename
attributes
vary
between
versions
of
a
plugin
,
they
can
be
used
both
as
a
fingerprinting
vector
and,
even
more
importantly,
as
a
trivial
way
to
determine
what
security
vulnerabilities
a
plugin
(and
thus
a
browser)
may
have.
It
is
thus
highly
recommended
that
the
description
attribute
just
return
the
same
value
as
the
name
attribute,
and
that
the
filename
attribute
return
the
empty
string.
A
MimeType
object
represents
a
MIME
type
that
is,
or
was,
explicitly
supported
by
a
plugin
.
The
MimeType
objects
created
by
a
user
agent
must
not
be
live
.
The
values
of
the
objects'
attributes
must
not
change
once
an
object
is
created,
except
when
updated
by
the
PluginArray
object's
refresh()
method.
The
type
attribute
must
return
the
valid
MIME
type
string
with
no
parameters
describing
the
MIME
type
.
The
description
and
suffixes
attributes
must
return
implementation-defined
(in
all
likelihood,
plugin
-defined)
strings.
In
each
case,
the
same
string
must
be
returned
each
time,
except
that
the
strings
returned
may
change
when
the
refresh()
method
updates
the
object.
If
the
values
returned
by
the
description
or
suffixes
attributes
vary
between
versions
of
a
plugin
,
they
can
be
used
both
as
a
fingerprinting
vector
and,
even
more
importantly,
as
a
trivial
way
to
determine
what
security
vulnerabilities
a
plugin
(and
thus
a
browser)
may
have.
It
is
thus
highly
recommended
that
the
description
attribute
just
return
the
same
value
as
the
type
attribute,
and
that
the
suffixes
attribute
return
the
empty
string.
Commas
in
the
suffixes
attribute
are
interpreted
as
separating
subsequent
filename
extensions,
as
in
"
htm,html
".
The
enabledPlugin
attribute
must
return
the
Plugin
object
that
represents
the
plugin
that
explicitly
supported
the
MIME
type
that
this
MimeType
object
represents
when
this
object
was
last
created
or
updated
by
refresh()
,
whichever
happened
most
recently.
Support in one engine only.
The
navigator.javaEnabled()
method
must
return
true
if
the
user
agent
supports
a
plugin
that
supports
the
MIME
type
"
application/x-java-vm
";
otherwise
it
must
return
false.